Stereoscopic projection system employing spatial multiplexing at an intermediate image plane

ABSTRACT

Projection systems and methods for providing stereoscopic images viewed through passive polarizing eyewear. The systems relate to projectors that create left and right eye images simultaneously and often as side-by-side images on the image modulator. The systems act to superimpose the spatially separated images on a projection screen with alternate polarization states. The embodiments are best suited to liquid crystal polarization based projection systems and use advanced polarization control.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application relates and claims priority to:

(1) provisional patent application Ser. No. 61/221,482, entitled“Stereoscopic Projection System Employing Spatial Multiplexing at anIntermediate Image Plane,” to Robinson et al., filed Jun. 29, 2009(“Robinson et al. Prov. Pat. App.”);

(2) provisional patent application Ser. No. 61/221,516, entitled,“Stereoscopic Projection System Employing Spatial Multiplexing Near theAperture Stop,” to Schuck et al., filed Jun. 29, 2009;

(3) provisional patent application Ser. No. 61/224,416, entitled“Stereoscopic Projection System Employing Spatial Multiplexing at anIntermediate Image Plane,” to Schuck et al, filed Jul. 9, 2009 (“Schucket al. Prov. Pat. App.”);

(4) provisional patent application Ser. No. 61/249,018, entitled,“Stereoscopic projection system employing spatial multiplexing at anintermediate image plane,” to Schuck et al., filed Oct. 6, 2009; and

(5) provisional patent application Ser. No. 61/256,854, entitled,“Stereoscopic projection system employing spatial multiplexing at anintermediate image plane,” to Schuck et al., filed Oct. 30, 2009;

all of which are herein incorporated by reference for all purposes.

TECHNICAL FIELD

The disclosed embodiments generally relate to projection systems and,more specifically, relate to projection systems that may selectivelyoperate in a stereoscopic mode and a non-stereoscopic mode.

BACKGROUND

Stereoscopic projection dates back to the early 20^(th) century and wasfirst seen in cinemas during the 1950s. These systems were film basedand were limited mechanically to modest ˜24 Hz frame rate. As such, itwas not possible to use temporal methods of providing flicker-freesequential left and right eye images for stereoscopy. Spatiallymultiplexed image display systems were therefore implemented. Somecomprised separate projectors while others employed a single projectorwith each frame comprising spatially separate left and right eye images.Complex frame dividing optics was used in this latter case tosuccessfully superimpose the images on the screen. Many systems weredeveloped and several commercially successful, as discussed by L. Liptonin Foundations of the Stereoscopic Cinema, Van Nostrand-Reinhold,Appendix 7, p. 260, 1982, which is hereby incorporated by reference.Unfortunately the quality of the stereoscopic experience wasinsufficient to draw customers leading to a reversal to 2D cinema in thelatter half of the century.

Stereoscopic projection has recently been revitalized with high qualityadvanced digital equipment encompassing capture, distribution anddisplay. To date the most successful projection system has beendeveloped and installed by RealD. Based on Texas instruments DigitalLight Processing (DLP) technology, systems provide time sequential leftand right eye images at flicker free rates. Incorporating a polarizationswitch in the projection path provides sequential left and right eyeimages for viewing through passive polarizing eyewear. While the systembased on DLP technology may provide good quality stereoscopic imagery,alternative projection platforms, such as those based on liquid crystal(LC) modulation, can also be considered. Desirable features of an LCprojector-based platform are potentially providing improved resolution,motion rendition, and optical polarization efficiencies. Presently, asingle LC projector does not however provide time-sequential images withsufficient frame rate to allow temporal left eye/right eye polarizationmodulation.

SUMMARY

Disclosed are stereoscopic projection systems and methods forstereoscopic projection.

Generally, according to an aspect, a projection system is operable toselectively project stereoscopic and non-stereoscopic projection modes.The projection system includes a relay lens subsystem, a stereoscopicmodule, a non-stereoscopic module, and a projection lens subsystem. Therelay lens subsystem is operable to receive input light from theprojection subsystem and convey the input light toward an intermediatelight path. The stereoscopic module is operable to receive the lightfrom the intermediate light path and process the light for stereoscopicprojection of left and right eye images having orthogonal polarizationstates. The non-stereoscopic module is operable to receive the lightfrom the intermediate light path. The projection lens subsystem isoperable to focus light from the stereoscopic module or thenon-stereoscopic module toward a screen. When the projection system isin a stereoscopic projection mode, the stereoscopic module is located inthe intermediate light path, and when the projection system is in anon-stereoscopic projection mode, the non-stereoscopic module is locatedin the intermediate light path.

Generally, according to another aspect, the stereoscopic projectionsystems may include a relay lens subsystem, a light splitting subsystem,a light combining subsystem, and a projection lens subsystem. The relaylens subsystem is operable to receive a stereoscopic image frame from aninput light path and convey the stereoscopic image frame to anintermediate image plane via a light directing element. The stereoscopicimage frame has first image area light and second image area light. Thelight splitting subsystem is operable to receive the stereoscopic imageframe at the intermediate image plane and split the first image arealight from the second image area light. The light splitting subsystem isalso operable to direct the first image area light on a first imagelight path, and to direct the second image area light on a second imagelight path. The light combining subsystem is operable to combine thefirst and second image area light, wherein the first image area lightthat is output from the light combining subsystem has a polarizationstate orthogonal to the second image area light. The projection lenssubsystem is operable to direct the first and second image area lighttoward a screen.

Other aspects, features and methods of stereoscopic and non-stereoscopicprojection are apparent from the detailed description, the accompanyingfigures and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic block diagram of an exemplary projection systemin a stereoscopic projection mode, in accordance with the presentdisclosure;

FIG. 1B is a schematic block diagram of an exemplary projection systemin a non-stereoscopic projection mode, in accordance with the presentdisclosure;

FIG. 2 is a schematic diagram of an embodiment of a stereoscopicprojection system, in accordance with the present disclosure;

FIG. 3 is a schematic diagram of an enlarged view of the image splittingand combining section of FIG. 2;

FIGS. 4A and 4B are drawings illustrating distorted side-by-side imagesas displayed on LC panels (4A) and anamorphic superposition on a screen(4B), in accordance with the present disclosure;

FIG. 5 is a schematic diagram illustrating another embodiment of astereoscopic projection system, in accordance with the presentdisclosure;

FIG. 6 is a schematic diagram illustrating another embodiment of astereoscopic projection system, in accordance with the presentdisclosure;

FIG. 7 is a schematic diagram of an enlarged view of the image splittingand combining section of FIG. 6;

FIG. 8 is a schematic diagram of an enlarged view of another exemplaryembodiment of an image splitting and combining section, in accordancewith the present disclosure;

FIG. 9 is a schematic diagram of a top down view of an embodiment of astereoscopic projection system, in accordance with the presentdisclosure;

FIG. 10 is an illumination footprint diagram at a screen for aprojection lens with and without cylindrical elements, in accordancewith the present disclosure;

FIG. 11 is a schematic diagram illustrating an alternative technique forenhancing image brightness with cylindrical elements by anamorphicallystretching an image to produce a brighter on-screen image, in accordancewith the present disclosure;

FIG. 12 is a schematic ray trace diagram illustrating a technique forconverting a spatially multiplexed 3D projection system to anon-multiplexed full resolution 2D system, in accordance with thepresent disclosure;

FIG. 13 is a schematic ray trace diagram illustrating another example ofa technique for converting the optical system from 3D mode to 2D fullresolution mode, in accordance with the present disclosure;

FIG. 14 is a schematic diagram illustrating an embodiment of a systemwith an external anamorphic converter lens located in the light pathafter the projection lens, in accordance with the present disclosure;

FIG. 15 is a schematic diagram illustrating another embodiment of asystem with an external anamorphic converter lens, in accordance withthe present disclosure;

FIG. 16 is a schematic diagram illustrating another embodiment of astereoscopic projection system, in accordance with the presentdisclosure;

FIG. 17 is a schematic diagram illustrating another embodiment of astereoscopic projection system, in accordance with the presentdisclosure;

FIG. 18 is a close-up view of the image splitting and combining assemblyin FIG. 17;

FIG. 19 is a schematic diagram of an enlarged view of another exemplaryembodiment of an image splitting and combining section, in accordancewith the present disclosure; and

FIG. 20 is a schematic diagram illustrating another embodiment of astereoscopic projection system, in accordance with the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1A is a schematic block diagram of an exemplary projection system100 in a stereoscopic projection mode, and FIG. 1B is a schematic blockdiagram of an exemplary projection system 100 in a non-stereoscopicprojection mode. FIGS. 1A and 1B illustrate the principle that astereoscopic module 150 or a non-stereoscopic module 180 may beselectively placed in a light path from a projector. A mechanicalassembly 145 may contain both the stereoscopic module 150 and thenonstereoscopic module 180, which may selectively slide back and forthbetween the stereoscopic mode and the nonstereoscopic mode according towhether the media type is stereoscopic imagery or not. Such aconfiguration may have practical application in cinematic environments,as well as home and office environments, requiring minimal technicalskill from an operator to place in the stereoscopic or a nonstereoscopicmode.

The exemplary projection system 100 includes a relay lens subsystem 130,optional light directing element 140, stereoscopic module 150,non-stereoscopic module 180, and projection lens subsystem 190.Stereoscopic module 150 may include a light splitting subsystem 160 anda light combining subsystem 170. Non-stereoscopic module 180 may includea 2D bypass subsystem 182, which may have an optical path length similarto the stereoscopic module 150. In an embodiment, the stereoscopicprojection system 100 may also include an audio visual source 134, acontroller subsystem 132, and a projection subsystem 110. The projectionsubsystem 110 may include, but is not limited to, an LC projectionsystem or a DLP projection system.

Although an exemplary multi-mode stereoscopic/nonstereoscopic system isshown herein, it should be apparent that this disclosure is not limitedto a multi-mode system. For example, the exemplary stereoscopicprojection system architecture shown herein may be applied to astereoscopic-only projection system that omits the nonstereoscopicmodule 180.

Referring to FIG. 1A, in a stereoscopic mode of operation, the audiovisual source 134 provides an audio visual signal 135 to thestereoscopic projection system 100. The controller subsystem 132 maytransmit a stereoscopic video signal 137 to the projection subsystem110. The projection subsystem 110 projects an image pair at the inputlight path 112. The relay lens subsystem 130 receives the input lightpath 112 and outputs intermediate light 114. An optional light directingelement 140 may direct the intermediate light 114 toward the lightsplitting subsystem 160 in the stereoscopic module 150. The lightsplitting subsystem 160 receives the intermediate light path 114 andoutputs light on a first image light path 116 and on a second imagelight path 118. The light combining subsystem combines the light fromfirst and second image light paths 116, 118 and directs substantiallyoverlapping first and second image light having orthogonal polarizationstates toward the projection lens subsystem 190, which is focused on ascreen 195. Various different optical architectures are presented hereinillustrating exemplary stereoscopic modules.

Referring to FIG. 1B, illustrating a nonstereoscopic mode of operation,the non-stereoscopic module 180 may be placed in the light path from thelight directing element 140, thus the 2D bypass subsystem 182 directsthe intermediate light path 114 toward the projection lens subsystem190. Various different optical architectures are presented hereinillustrating exemplary non-stereoscopic modules.

In an embodiment, common to both modes of operation, controllersubsystem 132 receives the audio visual signal 135 and outputs a controlsignal 136. The controller subsystem 132 may be operatively coupled tothe various subsystems, as shown. Controller subsystem 132 is operableto send control signals and receive feedback signals from any one of thevarious operatively coupled subsystems to adjust their respectiveoptical characteristics. The controller subsystem 132 may take inputfrom sensors, from the audio visual source 134, and/or from user inputto make adjustments (e.g., to focus or calibrate the stereoscopicprojection equipment on screen 195). The controller subsystem 132 mayalso control and/or drive an actuator 145 that moves thestereoscopic/non-stereoscopic modules 150/180 between stereoscopic andnon-stereoscopic configuration modes. Such an actuator 145 may be aprecise driving mechanism known to those of ordinary skill in the art,such as a stepper motor, and the like.

In another embodiment, the system 100 is a passive system and does notinclude active switching/control components. Thus, in such anembodiment, the system 100 does not include a control signal 136.

The relay lens subsystems (e.g., 130 in FIG. 1, et cetera) disclosedherein are assumed to be polarization-preserving and are operable towork in parallel with the projection lens subsystem (e.g., 190 in FIG.1, et cetera) to provide approximately panel-sized intermediate imagesat a modest distance from the lens output. Although the relay lenssubsystem is assumed to be a black box for all embodiments and itsdesign is not specific to the disclosures herein, examples of relaysystems may be found in commonly-assigned patent application Ser. No.12/118,640, entitled “Polarization conversion system and method forstereoscopic projection,” filed May 9, 2008, which is hereinincorporated by reference. In a similar manner, the projection opticsused to relay the intermediate images onto the screen are assumedconventional and specific designs are not provided since they are notgermane to the disclosure. In some embodiments, a polarizationpreserving projection lens may be used. An example of a polarizationpreserving lens is discussed by L. Sun et al. in Low Birefringence LensDesign for Polarization Sensitive Systems, Proc. SPIE Vol. 6288, hereinincorporated by reference.

The polarization aspects of the disclosure generally includeconditioning the light for efficient splitting and encoding of outputimages. Electronic aspects may generally include pre-distorting theimages to accommodate optical aberrations and allow anamorphic imagingtechniques to preserve aspect ratio of the original panel when only halfof the area is allocated to a full screen image. Generally, electronicalignment techniques may be used for on-screen image alignment. Opticalaspects of the disclosure generally cover techniques of physicallyseparating optical paths for each of the left and right eye images(e.g., the light splitting subsystem 160 in FIG. 1). In an embodiment,this splitting architecture is extended to enable superposition of theleft and right eye images prior to projection.

In an embodiment, it is assumed that the projection subsystem 110provides circular polarized light with green light having the oppositehandedness to red and blue. This is typical of three panel liquidcrystal projectors that use a combining X-cube. The color dependentlinear polarizations emanating from this element are routinelytransformed into circular polarization to avoid back reflections fromthe projection lens which may affect ANSI contrast. The preciseallocation of left handed or right handed polarization to the odd greenwavelengths is arbitrary, but may be pre-conditioned correctly. It isassumed here that effective correction may use a crossed matchingretarder, as this is the case for most commercial projectors on themarket. Though geared toward the mixed circular output, the systemembodiments should not be limited to the precise polarization statesassumed to emanate from the projector. The concepts covered here can beapplied to alternative projectors (e.g., DLP, etc.) since the creationof equivalent entrance polarizations can be easily provided by availablecomponents. For instance, ColorSelect® technology may map betweendefined wavelength dependent polarization states, and are described incommonly-assigned U.S. Pat. No. 5,751,384, herein incorporated byreference.

FIG. 2 is a schematic diagram of an embodiment of a stereoscopicprojection system 200. Generally, the system 200 may include aprojection subsystem 210, relay lens 230, light directing element 240,stereoscopic subsystem 250, and a projection lens 290. In this exemplarysystem 200, stereoscopic subsystem 250 may include light splittingsubsystem 260, first and second light directing elements 262, 264, andlight combining subsystem 270. Light combining subsystem 270 may includea polarization beam splitter (PBS) 272 and an achromatic rotator 242located on an input port of PBS 272. The system 200 may also includematched waveplates 222 a, 222 b and, wavelength-selective polarizationfilter 224 (e.g., a ColorSelect filter as taught in U.S. Pat. Nos.5,751,384 and 5,953,083, herein incorporated by reference), botharranged as shown, located in the light path between projectionsubsystem 210 and relay lens 230. Additionally, the system may includelight directing element 240 to direct light from relay lens subsystem230 toward the stereoscopic subsystem 250.

In operation, the relay lens subsystem 230 receives light from theprojection subsystem 210 at the input light path 212. In an embodiment,matched waveplates 222 a, 222 b and wavelength-selective polarizationfilter 224 are positioned on the input light path 212 between theprojection subsystem 210 and the relay lens subsystem 230.Alternatively, matched waveplates 222 a, 222 b may be positioned betweenthe relay lens subsystem 230 and the image splitting element 260, nearthe intermediate image plane 255. As another alternative, a firstmatched waveplate 222 a is positioned between the projection subsystem210 and the relay lens subsystem 230 (as shown) and a second matchedwaveplate 222 b is positioned between the relay lens subsystem 230 andthe light splitting element 260, near the intermediate image plane 255.The relay lens subsystem 230 outputs an intermediate light path 214toward a light directing element 240, that directs the light 214 towardan intermediate image plane 255 at the input of the light splittingelement 260. It should be noted that wherever the waveplate 222 b isplaced in the optical path, the wavelength selective filter 224 willfollow it somewhere downstream in the following light path, beforereaching the light combining subsystem 270.

Light directing element 240 is located in the light path 214 after therelay lens subsystem 230. Light directing element 240 may be a foldmirror (as shown here) or a prism. The light directing element 240redirects the light path 214 such that the optical axis of theprojection lens subsystem 290 is parallel to the optical axis of therelay lens subsystem 230. This improves system compatibility withexisting projection engines and theater geometries.

The light splitting subsystem 260 may be provided by highly reflectivesilver mirrors that are polarization preserving or a prism with mirroredor TIR surfaces. The light splitting subsystem 260 may alternatively beprovided by any other device that can split the light, for examplecircularly polarizing optical gratings may be used. The light splittingelement 260 is operable to split the intermediate light path 214 into afirst image light path 216 and a second image light path 218. In anembodiment, the first and second light directing elements 262, 264includes first and second mirrors configured to reflect their respectivefirst and second image light paths 216, 218 toward first and secondinput ports of light combining subsystem 270. The PBS 272 is operable tocombine the first and second image light paths 216, 218 into a thirdimage light path 219. The projection lens subsystem 290 receives thelight on the third image light path 219 and projects output image light292 toward a screen (not shown).

The exemplary system 200 includes superposition of oppositely polarizedleft- and right-eye image paths (e.g., first and second image lightpaths 216, 218) carried out at the interface of a PBS 272 before beingprojected by a single lens 290. By encoding the two images withorthogonal polarizations and directing them symmetrically into apolarizing beam splitting element 272 the two images appear to emanatefrom the same plane. A single polarization preserving projection lens290 can then project the images onto a screen.

In some embodiments, the polarization rotator element 274 may introducean optical path mismatch which may in practice be matched with dummymaterial at the other input port to the PBS 272.

“Wobulation” is a technical term for spatially dithering an image toincrease the perceived quality of the image. Spatial dithering involvespresenting an image at one instance in time, and presenting a spatiallyshifted image the next instance in time. The spatial shift is typicallya fraction of a pixel. The images from one instance to the next may bethe same (for a smoother overall image), or they may be different (for asmoother and sharper image). Methods for implementing wobulation includevibrating a mirror in the optical path (e.g., light directing element240) in synchronization with the two instances of the images asdiscussed in U.S. Pat. No. 7,330,298 to Bommerbach et al, which isherein incorporated by reference for all purposes. The mirror vibrationis modulated to produce an offset in one image that is generally afraction of a pixel relative to the other image. Another method is touse birefringent materials coupled with switching liquid crystalelements to induce the image shift, as discussed in U.S. Pat. No.5,715,029 to Fergason, which is herein incorporated by reference for allpurposes.

In an embodiment, the stereoscopic projection systems discussed aboveare altered to include wobulation. For example, in FIG. 2, the lightdirecting element 240 may be vibrated in synchronization with the imagedata to present spatially shifted images on-screen. Alternatively oradditionally, an LC cell and birefringent plate may be added to theoptical path prior to image splitting, to enable wobulation of bothimages together. An additional LC cell may be placed after thebirefringent plate (prior to the PBS 272) to restore the desiredorthogonal polarization states. Alternatively, the LC cells andbirefringent plate may be added after image splitting (prior to the PBS272) to enable wobulation separately for each image. Again, theadditional LC cell would be used after the birefringent plate to restorethe desired orthogonal polarization states prior to recombining thebeams in the PBS 272.

FIG. 3 is a schematic diagram of an enlarged view of the image splittingand combining section of FIG. 2, including matched waveplate 222 b,wavelength-selective filter 224, light directing element 240, lightsplitting subsystem (mirrored prism) 260, light directing elements 262,264, a PBS 272, and a rotator 274 for superimposing images. In thisexemplary embodiment, the matched waveplate 222 b and a Green/Magenta(G/M) wavelength-selective (Colorselect) filter 224 follow the relaylens 230 in a light path to provide higher contrast by substantiallyremoving relay lens ghost reflections. The diagram also illustrates aray trace analysis of the system.

The light directing element (mirror) 240 is placed at an angle such thatthe projection lens (not shown) and relay lens optical axes areparallel. A mirrored prism 260 is placed at the intermediate imagelocation 255 to split the two halves of the intermediate image. Amirrored prism 260 with very sharp corners (e.g., ˜50 um in width) maybe selected to minimize the unusable area at the intermediate image. AV-mirror arrangement (the combination of two flat mirrors) might also beutilized for the image splitting subsystem 260. Following the mirroredprism 260 are two folding mirrors 262, 264. The two folding mirrors 262,264 redirect the rays into the entrance surfaces of the PBS 272. Priorto the PBS 272, a rotator 274 is located in one path while an isotropicplate 276 (matched in optical thickness to the rotator) is placed inother path. The rotator 274 rotates one of the incident polarizationstates by 90 degrees such that the two states become orthogonal. A PBS272 combines the two orthogonal polarization states along the sameoptical path prior to the projection lens (not shown). The polarizingbeam splitter 272 is shown as a cube polarizing beam splitter. The PBSsurface can include of dielectric coating layers, or a wire gridpolarizer. Additionally, the PBS may be implemented with a plate inplace of the cube, where the plate is coated with appropriate dielectriclayers or wire grid coating. However, in this case the beam isdiverging, and thick plates will induce astigmatism in the image pathwhich may be corrected later in the system.

FIGS. 4A and 4B are drawings illustrating distorted side-by-side imagesas displayed on LC panels (4A) and their anamorphic superposition on ascreen (4B). Though drawn side-by-side, this embodiment may also coverover and under formats.

Anamorphic imaging could be carried out in the relay lens subsystem toprovide an intermediate image with correct aspect for each of the leftor right eye images. In this case, distortion expected in the complexrelay system may utilize electronic correction, or relative inversion ofthe paired images about the optical axis. Rotation of one of the imageswould then be performed with use of rotating separating prisms, asdiscussed by L. Lipton in Foundations of the Stereoscopic Cinemareferenced above.

Another related embodiment uses non-ideal separating mirrors in whichthe geometry would dictate polarization mixing, particularly if using atotal internal reflection (TIR) prism for redirecting circular polarizedbeams. For smaller systems, a TIR prism is preferred over mirrors forits higher reflectivity and smaller physical size. Its imparted phasedelay on reflection between s and p polarization components rapidlytransform polarization into a propagation dependent state. This leads ingeneral to projected image non-uniformity that may be corrected byintroducing intensity and bit depth loss. To reduce this problem to anacceptable level, linear polarization states can be created prior toentering the system. To a great extent, polarization is preserved sincethese states would closely resemble the s or p Eigen-states for themajority of rays present in the imaging system.

FIG. 5 is a schematic diagram of an embodiment of a stereoscopicprojection system 500 in which a delta prism 540 is used as a lightdirecting element, to provide a more compact system. Generally, thesystem 500 may include a projection subsystem 510, relay lens 530, andprojection lens 590. The system 500 may also include matched waveplates522 a, 522 b and, wavelength-selective polarization filter 524.

A delta prism 540 includes a triangular prism, with one face 542 coatedwith a mirror coating. Light enters a transmissive face 544, travels tothe second transmissive face 546, and totally internally reflects(TIR's) at the second transmissive face 546. The reflected light thentravels to the mirrored face 542, reflects, and travels to the firsttransmissive face 544. The light again TIR's at the input face 544 andtravels to the second transmissive face 546. The angles and refractiveindex of the prism are designed such that the light will exit the secondface 546 on this pass. In this case, the light is now incident on thelight splitting subsystem 560 at 45 degrees to the optical axis of therelay lens 530, the same as in the case of the mirror system in FIG. 2.The delta prism 540 provides a more compact solution than the mirror 240of FIG. 2. The delta prism 540 is desired to have low birefringence forefficiency and include anti-reflection coatings for the input face 544and output face 546.

Wobulation is enabled in this exemplary embodiment by rotating the prism540 about the optical axis of the relay lens 530. This rotation inducesa shift in image location on the screen. Alternatively, wobulation ofeach image might be enabled by vibrating the two re-directing mirrors562, 564 prior to the PBS 572.

FIG. 6 is a schematic ray tracing diagram of projection system 600showing the relay lens subsystem 630, delta prism 640, stereoscopicsubsystem 650, and projection lens subsystem 690. The stereoscopicsubsystem 650 includes a mirrored splitting prism 660, re-directingmirrors 662, 664, and the PBS 672 for combining the optical paths. Thematched waveplate 622 b, wavelength-selective filter 624, and rotator674 are also included for supporting the system operation.

FIG. 7 is a schematic ray trace diagram illustrating an enlarged view ofthe stereoscopic subsystem 650 of FIG. 6. The stereoscopic subsystem 650includes the mirrored splitting prism 660, mirrors 662, 664, PBS 672,and rotator element 674, as described above with reference to FIG. 6. Asshown in this example, the matched waveplate 622 b andwavelength-selective (or G/M) filter 624 are included after the relaylens 630. Polarized light enters and exits the delta prism 640 withsubstantially the same polarization. The mirrored prism 660 splits theimage, and the two flat mirrors 662, 664 redirect the images to the PBS672. Prior to the PBS 672, a rotator 674 changes the polarization of onepath while an isotropic plate 676 maintains the polarization in theother path. The PBS 672 combines the two paths into one path prior toprojection. Again, wobulation may be enabled by rotating the delta prism640 and/or vibrating the two redirection mirrors 662, 664.

FIG. 8 is a schematic diagram of another embodiment of a light directingelement 840 and light splitting and combining subsystem 860. Lightsplitting and combining subsystem 860 may include delta prisms 862, 864,PBS 872, and optional isotropic plate 876 and rotator 874. In thisexemplary embodiment, two delta prisms 862, 864 replace the reflectivesurfaces in the embodiment discussed in relation to FIG. 7 (660, 662,664). An optional rotator 854 may also be included for compensating skewray phase differences induced in the sets of delta prisms. Use of thedelta prisms 840, 862, 864, as opposed to the redirection mirrors,result in compacting the system. This allows a rotator 854 to beinserted between delta prism 840 and the two following delta prisms 862,864. A rotator 854 allows for near perfect compensation of phase errorsinduced by geometry effects of skew rays in the delta prisms 840, 862,864. Since the prisms all have substantially same geometry relative tothe ray paths, a rotator 854 between the prisms will optimallycompensate for the skew ray polarization effects. Wobulation, in thiscase, is enabled by rotating the first delta prism 840 and/or rotatingeach of the following delta prisms 862, 864.

FIG. 9 is a schematic ray trace diagram of a top down view of anembodiment of a stereoscopic projection system 900. This embodimentincludes a relay lens 930, light directing element 940, light splittingsubsystem 960, light combining subsystem 970, and projection lens 990.The projection lens 990 includes cylindrical elements for enablinganamorphic imaging. Cylindrical elements have been included in theprojection lens 990 to produce an anamorphically compressed image at thescreen, as disclosed in U.S. Pat. No. 3,658,410 to Willey, which isherein incorporated by reference for all purposes.

FIG. 10 is an illumination footprint diagram at the screen for theprojection lens with and without the cylindrical elements. Cylindricalelements enable anamorphic functionality. Region 1002 includesanamorphic elements and regions 1004 are without anamorphic elements. Inan embodiment, in the case of inclusion of the cylindrical elements, theoverall screen brightness is estimated to be approximately 57.5%brighter due to the addition of the anamorphic functionality whencompared to the standard projection lens case. The anamorphic elementsalter the aspect ratio of the projected image on screen.

FIG. 11 is a schematic diagram illustrating an alternative technique forenhancing image brightness with cylindrical elements by anamorphicallystretching an image to produce a brighter on-screen image. The image isstretched in the vertical direction to substantially fill the existingscreen area. Regions 1102 are the regions of anamorphic stretching.Stretching in the vertical direction allows the same projection lens tobe utilized for 2D and 3D presentations.

FIG. 12 is a schematic ray trace diagram illustrating a technique forconverting a spatially multiplexed 3D projection system to anon-multiplexed full resolution 2D system. In this exemplary embodiment,the splitting and recombining optics near the aperture stop are removedfrom the optical path, and the projection lens 1290 is pivoted such thatit is parallel with the relay lens 1230 optical axis. The projectionlens 1290 may be moved such that the intermediate image 1255 is locatednear the back focal length of the projection lens 1290. The projectionlens 1290 can then be focused and zoomed for proper presentation.

FIG. 13 is a schematic ray trace diagram illustrating another example ofa technique for converting the optical system from 3D mode to 2D fullresolution mode. In this embodiment, a portion of the splitting andrecombining optics are removed (the mirrored prism, mirrors, and PBS)and a 2D bypass subsystem 1380 is inserted into the optical path. Inthis example, the 2D bypass subsystem 1380 is a second delta prism. Thesecond delta prism 1380, in combination with the first delta prism 1340,vertically shifts the optical axis of the light path coming from therelay lens 1330 to align with the projection lens 1390 optical axis. Theprojection lens 1390 may move along the optical axis to re-focus theimage. The prisms do not have to be delta prisms; rather, prisms ormirrors that redirect the optical axis at approximately 45 degrees maybe used. Alternative prisms include the TIR prism type shown in FIG. 16.

FIG. 14 is a schematic ray trace diagram illustrating an embodiment of asystem 1400 with an external anamorphic converter lens 1495 located inthe light path after the projection lens 1490, see, e.g., U.S. Pat. No.5,930,050 to Dewald (the magnification in FIG. 14 has opposite polarityto Dewald).

FIG. 15 is a schematic ray trace diagram illustrating another embodimentof a system 1500 with an external anamorphic converter lens 1595. Asshown, for 3D operation, the anamorphic converter 1595 (i.e. ananamorphic afocal converter) is put in place after the projection lens1590 to produce a brighter 3D image from the multiplexed panel. For 2Dfull resolution operation, the anamorphic converter 1595 may be removedfrom the optical path to allow the non-multiplexed full 2D panelresolution to be presented without anamorphic distortion. FIG. 14depicts an anamorphic converter with magnification 0.5× in thehorizontal direction, while FIG. 15 depicts an anamorphic converter withmagnification 2× in the vertical direction.

FIG. 16 is a schematic ray trace diagram illustrating another embodimentof a stereoscopic projection system 1600. System 1600 further includes aBravais subsystem 1632 implemented at the output of the relay lens 1630and prior to the image splitting subsystem 1660. The TIR prism 1640 hasbeen changed to accommodate the non-telecentric ray bundles emergingfrom the Bravais 1632. An optional cylindrical field lens 1636 is alsoshown for creating telecentric bundles, should a telecentric projectionlens be used. The anamorphic stretch has been implemented in thevertical direction, allowing the same projection lens 1690 to beutilized for both 2D and 3D presentations with little or no change inprojection lens zoom setting.

Bravais optical systems have been utilized to provide anamorphic stretchor compression along one direction of an image as disclosed by W. Smithin Modern Optical Engineering, p. 272, McGraw-Hill 1990 (describing theuse of Bravais optics in motion pictures work), which is hereinincorporated by reference for all purposes. Bravais systems comprise apositive and negative cylindrical element separated by a finite distanceand located in the finite conjugate of a lens system.

A Bravais system might be inserted near the panel, close to the relaylens output, or close to the projection lens input. The polarization andcolor management optics make inserting Bravais optics near the paneldifficult. The Bravais system shortens the projection lens back focallength (BFL), and a long BFL is preferred for inserting the PBS,splitting prism, and mirrors.

FIG. 17 is a schematic ray trace diagram illustrating another embodimentof a stereoscopic projection system 1700 that is similar to theembodiment shown in FIG. 16, with a difference being that the mirroredprism and folding mirrors have been replaced with more compact deltaprisms 1760. System 1700 also includes a Bravais subsystem 1732implemented at the output of the relay lens 1730.

FIG. 18 is a close-up view of the image splitting and combining assemblyin FIG. 17, specifically showing a close-up view of the paraxial Bravaissystem 1732, filter 1714, field lens 1736, and prisms 1764, 1762. TheBravais anamorphic lens 1732 (depicted as a paraxial lens) follows therelay lens. A matched quarter-wave plate 1722 b and wavelength-selectivefilter 1714 follow the Bravais 1732. A TIR turning prism 1734 is next,followed by a cylindrical field lens 1736 to provide for telecentricityat the intermediate image. Two modified delta prisms 1762, 1764 followthe cylindrical field lens 1736. The delta prisms 1762, 1764 have cutcorners near the intermediate image to facilitate image splitting whilemaintaining clear aperture through the prism for the marginal rays. APBS 1772 follows the two delta prisms and combines the images. A rotator1774 is included in one of the optical paths after the delta prisms, andoptional cleanup polarizers (not shown) may also be implemented betweenthe delta 1762, 1764 and PBS 1774. The entire assembly is compact andaffords a small back focal length in the projection lens. This aids inreducing cost and/or improving performance of the projection lens.

FIG. 19 is a close-up view of another image combining assembly that issimilar to the embodiment shown in FIG. 18, but is adapted fornon-anamorphic systems (i.e. systems without the Bravais anamorphiclens). This embodiment includes filter 1914, matched quarter-wave plate1922 b, TIR prism 1934, prisms 1964, 1962, PBS 1972, and rotator 1774.In this embodiment, the cylindrical field lens 1736 of FIG. 17 is notincluded, and may be utilized in non-anamorphic systems (i.e. systemswithout the Bravais anamorphic lens).

FIG. 20 is a schematic ray trace diagram illustrating another embodimentof a 3D lens system 2000. In this embodiment, an anamorphic telecentricrelay lens 2099 is inserted between the standard relay lens 2030 and theprojection lens 2090. The anamorphic relay lens 2099 creates a realimage of the intermediate image produced by the standard relay lens2030. The projection lens 2090 then projects an image of the anamorphicrelay lens's 2099 image onto the screen 2095.

In this embodiment, the anamorphic telecentric relay lens 2099 may be atelecentric relay lens with an afocal anamorphic converter located nearits aperture stop. The afocal anamorphic converter may be an afocalconverter implemented with cylindrical lenses. The cylindrical lensesmay change the magnification of the relay in one aspect (e.g. 2×magnification vertically) while having a unity magnification in theorthogonal aspect (e.g. 1× magnification horizontally). In any of theanamorphic implementations, the magnification in each aspect may bedifferent to be considered anamorphic (i.e. the aspects can bemagnifications other than unity magnification). If both aspects havemagnification not equal to 1, then toric elements are desirable in theconverter, or multiple cylindrical elements which have orthogonal axesof rotation may be used. The anamorphic relay is preferably telecentricto maintain light throughput and contrast. The telecentric anamorphicrelay lens 2099 is shown between the prism assembly 2060 and projectionlens 2090 in this exemplary embodiment, but it may also be implementedbetween the standard relay lens 2030 and prism assembly 2060.

Note that in this embodiment a cylindrical field lens is not included atthe first intermediate image. When the anamorphic converter is placednear the aperture stop of a lens, it is operating on collimated beams,an advantage in terms of aberration correction. Telecentricity can thusbe maintained without the use of a field lens. Additionally, theanamorphic converter may be implemented near the aperture stop of thefirst relay lens or the projection lens, moving the anamorphic functionto one of those locations, which may allow for the lack of theanamorphic telecentric relay. An advantage of a system utilizing theanamorphic telecentric relay is that the anamorphic telecentric relaymay be removed, and the system may operate with equal magnification inall directions (e.g. for 2D presentation using the full panelresolution). U.S. Pat. No. 6,995,920 describes a telecentric anamorphicrelay lens for use with camera (image taking) lenses, and is hereinincorporated by reference.

It should be appreciated that a Bravais anamorphic lens may be added tothe various embodiments disclosed herein in order to improve the lumenoutput of the system. The Bravais can be placed after the relay lens andbefore the splitting prisms. The Bravais magnifies the intermediateimage by 2× in the vertical direction and 1× in the horizontaldirection, allowing the full panel size to be utilized in 3D mode. Ifthe Bravais is removed, and the splitting prisms and projection lensesare translated vertically such that the entire intermediate image passesthrough a single TIR prism and single projection lens, the fullresolution image from the panel can be utilized for 2D presentations.

Additionally, it should be appreciated that external anamorphic afocalconverters may be applied to the various embodiments disclosed herein inorder to improve the lumen output of the system. Such externalanamorphic converters can be located after the projection lenses.Alternatively, the projection lenses themselves may be made anamorphic(e.g. as a single projection lens is made anamorphic in U.S. Pat. No.5,930,050, herein incorporated by reference) to improve the lumenoutput.

While various embodiments in accordance with the disclosed principleshave been described above, it should be understood that they have beenpresented by way of example only, and are not limiting. Thus, thebreadth and scope of the invention(s) should not be limited by any ofthe above-described exemplary embodiments, but should be defined only inaccordance with the claims and their equivalents issuing from thisdisclosure. Furthermore, the above advantages and features are providedin described embodiments, but shall not limit the application of suchissued claims to processes and structures accomplishing any or all ofthe above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 C.F.R. 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theinvention(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” such claims should not be limited by the languagechosen under this heading to describe the so-called technical field.Further, a description of a technology in the “Background” is not to beconstrued as an admission that technology is prior art to anyinvention(s) in this disclosure. Neither is the “Summary” to beconsidered as a characterization of the invention(s) set forth in issuedclaims. Furthermore, any reference in this disclosure to “invention” inthe singular should not be used to argue that there is only a singlepoint of novelty in this disclosure. Multiple inventions may be setforth according to the limitations of the multiple claims issuing fromthis disclosure, and such claims accordingly define the invention(s),and their equivalents, that are protected thereby. In all instances, thescope of such claims shall be considered on their own merits in light ofthis disclosure, but should not be constrained by the headings herein.

What is claimed is:
 1. A stereoscopic projection system, comprising: arelay lens subsystem operable to receive a stereoscopic image frame froma projection subsystem along an input light path and convey thestereoscopic image frame to an intermediate image plane, thestereoscopic image frame having first image area light and second imagearea light; a light splitting subsystem operable to receive thestereoscopic image frame at the intermediate image plane and split thefirst image area light from the second image area light, to direct thefirst image area light on a first image light path, and to direct thesecond image area light on a second image light path; a light combiningsubsystem operable to combine the first and second image area light,wherein the first image area light that is output from the lightcombining subsystem has a polarization state orthogonal to the secondimage area light; and a projection lens subsystem operable to direct thefirst and second image area light toward a screen.
 2. The stereoscopicprojection system of claim 1, wherein the light combining subsystemcomprises a polarization beam splitter (PBS).
 3. The stereoscopicprojection system of claim 1 wherein the projection lens subsystemcomprises a single projection lens.
 4. The stereoscopic projectionsystem of claim 1, further comprising a liquid crystal (LC) projector.5. The stereoscopic projection system of claim 4, further comprising amatched waveplate located on the input light path before the relay lenssubsystem, the matched waveplate being substantially dispersion matchedto a waveplate within the LC projector.
 6. The stereoscopic projectionsystem of claim 4, further comprising a matched waveplate located on theintermediate light path after the relay lens subsystem, the matchedwaveplate being substantially dispersion matched to a waveplate withinthe LC projector.
 7. The stereoscopic projection system of claim 1,further comprising: a wavelength selective polarization filter locatedon one of the input light path and intermediate light path.
 8. Thestereoscopic projection system of claim 1, further comprising a quarterwave plate located on an output light path.
 9. The stereoscopicprojection system of claim 1, wherein the light splitting subsystemcomprises first and second mirrors.
 10. The stereoscopic projectionsystem of claim 1, wherein the light splitting subsystem comprises oneof a total internal reflection prism, a mirrored prism, and a pair oftotal internal reflection prisms.
 11. The stereoscopic projection systemof claim 1, wherein the projection lens subsystem comprises apolarization beam splitter (PBS) and a single projection lens; whereinthe PBS is operable to combine the first and second image area light;wherein the single projection lens is operable to project the combinedfirst and second image area light toward the screen; and wherein thefirst and second image area light substantially overlap on the screen.12. The stereoscopic projection system of claim 1, wherein thestereoscopic image frame is conveyed to the intermediate image plane viaa light directing element.
 13. The stereoscopic projection system ofclaim 12, wherein the light directing element comprises one of a mirrorand a prism.
 14. A projection system operable to selectively projectstereoscopic and non-stereoscopic projection modes, comprising: a relaylens subsystem operable to receive input light from a projectionsubsystem and convey the input light toward an intermediate light path;a stereoscopic module operable to receive the light from theintermediate light path and process the light for stereoscopicprojection of left and right eye images having orthogonal polarizationstates; a non-stereoscopic module operable to receive the light from theintermediate light path; a projection lens subsystem operable to focuslight from the stereoscopic module or the non-stereoscopic module towarda screen; and wherein when in a stereoscopic projection mode, thestereoscopic module is located in the intermediate light path, andwherein when in a non-stereoscopic projection mode, the non-stereoscopicmodule is located in the intermediate light path.
 15. The projectionsystem of claim 14, further comprising a selector for selecting betweenthe stereoscopic mode and the non-stereoscopic mode.
 16. The projectionsystem of claim 14, further comprising a mechanism operable toselectively locate the stereoscopic module into the intermediate lightpath when in the stereoscopic mode, and locate the non-stereoscopicmodule into the intermediate light path when in the non-stereoscopicmode.
 17. The projection system of claim 16, further comprising anactuator operable to move the mechanism between the stereoscopic modeand the non-stereoscopic mode.
 18. The projection system of claim 14,further comprising a light directing element located after the relaylens subsystem, operable to direct light toward on the intermediatelight path.
 19. The projection system of claim 18, wherein the lightdirecting element is selected from the group comprising a mirror, and aprism.
 20. The projection system of claim 14, wherein the stereoscopicmodule comprises: a light splitting subsystem operable to: receive astereoscopic image frame having first and second image area light at anintermediate image plane, split the first image area light from thesecond image area light, to direct the first image area light on a firstimage light path, and to direct the second image area light on a secondimage light path; and a light combining subsystem operable to combinethe first and second image area light, wherein the first image arealight that is output from the light combining subsystem has apolarization state orthogonal to the second image area light.
 21. Thestereoscopic projection system of claim 14, further comprising a liquidcrystal (LC) projector.
 22. The stereoscopic projection system of claim14, further comprising a quarter wave plate located on an output lightpath.